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Avalanche Forecast

Archived

Feb 20th, 2018–Feb 21st, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Sea To Sky.

The snow is heavily wind-affected. Stick to sheltered trees to find the best and safest riding.

Confidence

High - The weather pattern is stable

Weather Forecast

A fairly benign weather pattern is expected through the forecast period. Wednesday: Cloudy with isolated flurries. Alpine temperatures near -12 and ridgetop winds light to moderate from the West.Thursday: Mostly sunny with some cloud cover. Alpine temperatures near -10 and ridgetop winds light to moderate from the North.Friday: Mainly cloudy with some new snow. Alpine temperatures near -9 and ridgetop winds strong from the southwest.

Avalanche Summary

On Monday, numerous wind slabs and cornice failures were reported. Most wind slabs were reactive to rider triggers, and explosive control up to size 2 on all aspects above 1800 m. The cornice failures were triggered by explosives but not pulling a slab or entraining much mass from the slopes below. With little change in the weather forecast natural avalanche activity will subside, but human triggers remain possible.

Snowpack Summary

In exposed terrain, strong north winds have scoured north facing slopes and loaded south facing slopes. In sheltered terrain, especially in the trees the cold weather is preserving 30-40 cm of low density snow. A crust layer can be found beneath the storm snow on sun-exposed slopes and below 1900 m, which has supported some wide propagations in recent storm slab avalanches. Deeper in the snowpack, avalanche professionals are still monitoring the mid-January crust. This layer is now 150-200 cm deep, but a heavy trigger (cornice?) or the next major storm (warming and loading) could potentially wake up this layer.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.